Oxygen concentration of gut luminal contents varies post-prandially in growing pigs

The oxygen (O₂ ) concentration of gastrointestinal tract (GIT) contents decreases distally, but little is known about how O₂ concentrations are influenced by ingestion of a meal. The O₂ concentration in luminal contents at different GIT locations (stomach [cardia and pylorus], proximal, mid- and distal small intestine and caecum) and how these concentrations changed post-prandially were determined. Fifty entire male pigs (22 kg bodyweight at the start of study) were fed semi-synthetic diets containing casein, α-lactalbumin, whey protein isolate or zein as the sole source of protein for 8 days. A further group of pigs received the casein diet for six days and a semi-synthetic protein-free diet for a further 2 days. On day 8, pigs (n = 2 per diet and time point) were euthanized post-prandially (0, 1, 2, 4 and 6 h), and the stomach, small intestine and caecum were isolated and O₂ determined in the GIT contents. Observations at each time point were averaged across the diets (n = 10). The mean O₂ concentration was markedly higher (p ≤ 0.05) in the stomach compared with the rest of the GIT. The O₂ concentration was similar in the small intestinal regions (p > 0.05; 1.0%-1.1%) and the caecum (0.9%), apart for the proximal small intestine which had a 24% higher (p ≤ 0.05) O₂ concentration than the caecum. The mean O₂ concentration in the GIT varied post-prandially (p ≤ 0.05). The O₂ concentration in the cardia decreased 1.8%/h over the first two hours post-feeding and thereafter increased 0.3%/h (p ≤ 0.05). In the caecum, the O₂ concentration was constant during the first 4 h and thereafter increased slightly (p ≤ 0.05). The flow of food through the GIT influenced both the concentration and amount of O₂ in GIT luminal contents.